Shattering the energy barrier.

Describes how methods used in widespread energy efficient residential buildings in Germany are now being applied to larger buildings. Germany's Passiv Haus Institut has become a leading centre in developing a specification for the next generation of energy efficient buildings - the Passive House Standard. In 400 residential building the standard has reduced total energy consumption to 12% of the UK norm. Describes how this approach has been applied to a 2,200 m2 office and factory in Colbe, Marburg. The three-storey structure was completed in autumn 1998. It is a straightforward combination of concrete-frame external walls with calcium silicate block infill, in situ concrete intermediate floors and a timber I-beam roof. The most heavily-glazed wall is steel-frame. The timber-clad external wall insulation panels are bolted to the outside of the frame. To reduce air leakage, a sealed polyethylene air vapour barrier is fitted between the wall cladding panels and the frame. Doors are insulated as well as walls. The office reached the space heating energy budget of 15 kWh/m2y by vigorous intervention from the PHI. The PHI standard for air leakage is 0.6 ac/h at 50 Pa. The mechanical ventilation/heat recovery system uses four cross-flow exchangers in series, giving 80% overall efficiency. Utilising a system with no risk of leakage between the inlet and exhaust airstreams allowed all the toilets to be connected to the central MVHR system; there are no other fans except in the kitchen, which has a separate exhaust. The building has four parallel earth-preheating tubes. The building needs a small input of heat in winter, which is simply added to the normal flow of ventilationair. The gas is burned not in a condensing boiler but in a small chp system. This is the size of a lawnmower engine with outputs of 5 kW(e) and 12 kW(t). This means that the heating system installed capacity is 5 kW/m2 floor area which is 75% below the 21 W/m2 of the UK Elizabeth Fry Building, which itself broke UK records. In hot summer weather small clerestory windows are opened at nights to cool the building mass and are almost closed up during hot days. This strategy has consistently kept the building interior air below 27 Deg C even when the outside temperature reached 33 Deg C.